IRRADIATION TEMPERATURE EFFECTS ON HYDROGEN-ATOM REACTIONS UPON RADIOLYSIS AND PHOTOLYSIS AT 4.2-K AND 77-K OF NEOPENTANE CONTAINING VARIOUS ADDITIVES AS STUDIED BY ELECTRON-SPIN RESONANCE

The cause of the suppression of the selective formation of solute radicals at 4.2 K in the radiolysis of neopentane containing additives has been studied by the electron spin resonance technique. The suppression of solute radical formation is characteristic of reactions of hydrogen atoms with solutes and becomes prominent with decreasing irradiation temperature, suggesting that the migration of hydrogen atoms to solute molecules is suppressed below 77 K. The suppression of the solute radical yield at 4.2 K in the high concentration range suggests that hydrogen atoms are almost immobilized at their place of birth and react only with surrounding molecules at 4.2 K. On the other hand, formation of solute radicals from the reactions of electrons and holes was not suppressed at 4.2 K. The behaviors of hydrogen atoms produced from HI photolysis in neopentane matrices were essentially the same as those in the radiolysis, indicating that the immobilization of hydrogen atoms at 4.2 K are mainly related to the nature of the matrices. © 1979 American Chemical Society.